1. Technical Field
The present invention relates to an axial flow fan in which a shape of a positive pressure surface of a blade of an impeller is improved.
2. Description of Related Arts
The axial flow fan includes a plurality of blades in a radial shape on an outer circumference of a hub serving as a rotation center. Since the axial flow fan has a simple structure, the axial flow fan is widely used in a personal computer (PC), a cooling fan for a server, a ventilation fan or the like.
Generally, the axial flow fan has blowing characteristics in which a wind quantity is high and a static pressure is low. In order to improve the blowing characteristics of the axial flow fan to reduce noise, various schemes have been performed on the structure of the blades.
As a technique related to the blade structure of the axial flow fan, an axial flow fan is disclosed in which a plurality of blades is included on an outer circumference of a hub serving as a rotation center, a plurality of dimples is formed on a negative pressure surface of each blade, and a relationship of 0.15≦d/φ≦0.3 is set when assuming a depth of the dimple to d and a hole diameter of the dimple to φ (for example, see JP 5-332294 A).
The technique of JP 5-332294 A suppresses a development of a boundary layer and a separation of a flow on the negative pressure surface of the blade, and plans the reduction of the noise of the axial flow fan and the improvement in aerodynamic performance, by forming the plurality of dimples on the negative pressure surface of each blade on a predetermined condition.
Furthermore, an axial flow fan is disclosed which is formed by providing a plurality of protrusions on a pressing surface of the blade, and by forming a streamlined blade shape by a surface formed by joining tops of the protrusions and the negative pressure surface of the blade (for example, JP 11-37092 A).
The technique of JP 11-37092 A provides an axial flow fan that has a high blowing efficiency and a low noise, and is lightweight, by providing a plurality of protrusions on the pressing surface (a positive pressure surface) so as to form the streamlined blade shape by the negative pressure surface of the blade.
However, according to the techniques of JP 5-332294 A and JP 11-37092 A, the reduction of the electric power consumption of the axial flow fan is not examined at all, and even when the blowing efficiency is improved and the noise is reduced, the technical value is reduced by half when the electric power consumption increases.
Recently, along with the maintenance promotion of the internet and the infrastructure, a large server has spread. A plurality of about forty cooling fans is attached to the casing of the large server. A power source of the plurality of cooling fans is normally supplied from a single power source device stored in the casing, and thus load to the power source device is great. Thus, when the electric power consumption of each of the cooling fans can be lowered even a little, it is possible to greatly lower the load to the power source device as a whole of the cooling fans.
The present invention was made in view of the above-mentioned circumstances, and an object thereof is to provide an axial flow fan capable of improving the blowing efficiency and the static pressure efficiency and reducing the electric power consumption.